As offshore wind farms are moving further offshore and into areas with more complicated ground conditions, alternative offshore foundation concepts are becoming increasingly relevant. Drilled foundations are employed in regions with stiff soil conditions where traditional installation methods, such as impact driving, vibration, or gravity-based foundations, are no longer feasible. This paper presents different drilled foundation concepts, where the design methodology of one concept involving a grout socket is explained in detail. The grout socket is verified through an innovative combination of advanced threedimensional finite element models and existing grouted connection design standards.
With the increasing demand of offshore wind farms worldwide it has become relevant to extend the geographical application of pile foundations to regions where the most common installation methods are no longer feasible. Pile driving and vibration installation procedures are limited to regions with relatively soft soil conditions, to reach the desired embedment depth without inducing significant damage to the structure. The drilled pile foundation concept is developed to extend the application of offshore wind turbines to regions with stiff soil conditions where neither traditional driven piles nor gravity-based foundation are feasible. Different variants of the drilled pile foundation concept are presented and evaluated. An essential aspect of drilled foundation is the pile installation and the corresponding marine operations.
Currently, no explicit guidelines exist for drilled foundations. This paper presents the design methodology and verification procedure behind a drilled foundation concept and addresses the main critical practical aspects related to the installation. The design of drilled foundations for offshore wind turbines is a multi-disciplinary effort involving both theoretical aspects of soil mechanics and geotechnical as well as structural design. The design methodology and verification process are outlined for one of the drilled foundation concepts. The elaborated concept involves drilling of an oversized hole, wherein the pile is placed. To ensure a tight and direct load transfer, the annulus between pile and the surroundings is filled with grout. The focus of this paper is mainly on the structural design of the grout.